Brushless D.C. motor driving and controlling method and apparatus therefor and electrical equipment

ABSTRACT

When a brushless D.C. motor 3, 13 is driven by voltage-fed inverters 2, 5, 12, 20, a conducting interval of the voltage-fed inverters 2, 5, 12, 20 is determined to be greater than 120° and equal or less than 180° by electrical angle so that improvement in efficiency and enlargement in operating range of the brushless D.C. motor is achieved with simple and cheap controlling.

TECHNICAL FIELD

The present invention relates to a brushless D.C. motor driving andcontrolling method and apparatus therefor. More particularly, thepresent invention relates to a brushless D.C. motor driving andcontrolling method and apparatus which drive a brushless D.C. motorusing voltage-fed inverters, and to electrical equipment which employs abrushless D.C. motor as a driving source which is driven and controlledby the brushless D.C. motor driving and controlling apparatus.

BACKGROUND ART

A brushless D.C. motor is known as a motor having higher efficiency incomparison to an A.C. motor. The rotor of a brushless D.C. motor isequipped with permanent magnets instead of rotor windings, thereforesecondary copper losses caused by currents flowing in the rotor windingsis eliminated.

It is known that a brushless D.C. motor has a remarkable efficiencyimproving effect in comparison to an A.C. motor when the brushless D.C.motor has a medium or small capacity which is equal or less than severaltens kW.

In a brushless D.C. motor driving system having such capacity,voltage-fed inverters or current control type inverters are employed asinverters for driving a brushless D.C. motor. Wherein, the currentcontrol type the inverters has a main circuitry arrangement which is thesame to that of voltage-fed inverters, and controls the inverters so asto determine a motor current to be a desired value.

A system which drives a brushless D.C. motor using the voltage-fedinverters, is mainly used on devices which require efficient powerconsumption (improvement in efficiency), and is manufactured in largequantities, such as air conditioners, vacuum cleaners, electric washersand others. Therefore, a waveform having a conducting interval which is120° by electrical angle, is employed as a waveform control in invertersfrom the point of view of easiness in controlling. And, a system isemployed which has a simple arrangement and which is cheap. (refer to"Microcomputer-Controlled Brushless Motor Without a Shift-MountedPosition Sensor", T.Endo et. al., IPEC-Tokyo'83,pp.1477-1488,1983:"Controlling Apparatus of a Brushless D.C. Motor", Nagata et. al.,Japanese Patent Laid Open Gazett Tokuganhei 5-72197: "P.M.BrushlessMotor Drives:A self-Commutating System without Rotor-Position Sensors",P.Ferraris et. al.,Ninth Annual Symposium-Incremental Motion ControlSystems and Devices,pp.305-312,1980) Further, Magnetic pole positiondetection by detection of induced voltages of a motor, or by a magneticpole position detection sensor having a simple arrangement and employingHall elements and the like is employed in detecting magnetic poleposition of a brushless D.C. motor. A rotational position sensor whichis expensive, such as a rotary encoder and the like, is not employed asit is not economical.

A system which drives a brushless D.C. motor using the current controltype inverters, is typically applied to machine tools, servo-motor foran industrial robot, and others which require rapid torque response andthe low torque ripple.

In this system, a closed loop arrangement is employed in which a controlcircuitry determines output voltages of inverters so that currentwaveforms are the desired waveforms. This is so because the currents andtorques of a brushless D.C. motor are functions of rotational positionand are in proportional relationship. Therefore, the system has anexpensive system arrangement which employs a precision sensor fordetecting rotational position of a motor, current detectors foraccurately controlling motor currents and a controller which can performhigh-speed processing. Further, output voltages of inverterscontinuously vary because the inverters are controlled instantaneouslyin response to the conditions of the motor.

In the system in which a brushless D.C. motor is driven usingconventional voltage-fed inverters, a switch of each phase of invertersis turned on for only an electrical angle of 120° in spite of positiveand negative electrical angles of 180°, respectively. Therefore, theterm of the remaining electrical angle of 60° (the term of electricalangle of 120° for one cycle) is non-controlled condition.

Consequently, inverters cannot output desired voltages during the termof non-controlled condition so that the available rate of d.c. voltagein the inverters is low. And, terminal voltages of a brushless D.C.motor become small and an operating range becomes narrower (a maximumnumber of revolution becomes smaller) due to the low available rate ofd.c. voltage.

Further, motor currents should be increased for obtaining an outputwhich is the same to that of a motor which is supplied terminal voltageswhich are not lowered, because the terminal voltages are lowered. As aresult, joule losses which are caused by resistances of motor windings,increase so that efficiency of a brushless D.C. motor cannot be improvedto an expected degree.

Although, permanent magnets are installed to a rotor of a brushless D.C.motor so that each permanent magnet corresponds to the electrical angleof 180°, currents can be flowed in desired directions for only anelectrical angle of 120° so that available rate of magnetic flux issmall. In other words, motor currents should be increased for obtaininga torque which is the same to that of a motor which does not have theavailable rate of magnetic flux lowered. As a result, joule losses whichare caused by resistances of motor windings, increase so that efficiencyof a brushless D.C. motor cannot be improved to an expected degree.

DISCLOSURE OF THE INVENTION

The present invention was made in view of the above-mentioned problems.

It is an object of the present invention to supply a brushless D.C.motor driving and controlling method and apparatus therefor whichimprove available rates of voltage of voltage-fed inverters and motorflux using simple and cheap control, and which achieves higherefficiency and enlargement of the operating range of a brushless D.C.motor.

It is another object of the present invention to supply to electricalequipment which employs a brushless D.C. motor as a driving source, amotor which is driven and controlled by the brushless D.C. motor drivingand controlling apparatus.

A brushless D.C. motor driving and controlling method according to claim1 is a method which determines a conducting interval of voltage-fedinverters to be a predetermined interval which is more than 120° andequal or less than 180° by electrical angle.

A brushless D.C. motor driving and controlling method according to claim2 is a method which modulates outputs of voltage-fed inverters so as tooutput pulse signals, each pulse signal having constant pulse widthwithin an entire conducting interval.

A brushless D.C. motor driving and controlling method according to claim3 is a method which employs a rotor which includes permanent magnets inthe interior of the rotor, as a rotor of a brushless D.C. motor.

A brushless D.C. motor driving and controlling method according to claim4 is a method which controls voltage-fed inverters so that a phase ofinverter output voltage is advanced from a phase of the inverter outputvoltage with respect to an induced voltage of a brushless D.C. motor,the latter phase being a phase in which a brushless D.C. motor currentand the induced voltage of the brushless D.C. motor are in phase.

A brushless D.C. motor driving and controlling method according to claim5 is a method which determines a conducting interval of voltage-fedinverters to be 180° by electrical angle.

A brushless D.C. motor driving and controlling method according to claim6 is a method which obtains a first voltage at a neutral point from anend of resistors, which are connected to each output terminal ofvoltage-fed inverters, obtains a second voltage at a neutral point fromone ends of stator windings of a brushless D.C. motor, and detects amagnetic pole position of a rotor of the brushless D.C. motor based upona difference between the first voltage and the second voltage.

A brushless D.C. motor driving and controlling method according to claim7 is a method which determines a conducting interval of voltage-fedinverters to be a predetermined interval which is more than 120° andless than 180° by electrical angle.

A brushless D.C. motor driving and controlling method according to claim8 is a method which determines a conducting interval of voltage-fedinverters to be a predetermined interval which is equal or more than140° and equal or less than 170° by electrical angle.

A brushless D.C. motor driving and controlling apparatus according toclaim 9 includes a conducting interval determining means for determininga conducting interval of voltage-fed inverters to be a predeterminedinterval which is more than 120° and equal or less than 180° byelectrical angle.

A brushless D.C. motor driving and controlling apparatus according toclaim 10 further includes a modulating means for modulating outputs ofvoltage-fed inverters so as to output pulse signals, each pulse signalhaving constant pulse width within an entire conducting interval.

A brushless D.C. motor driving and controlling apparatus according toclaim 11 employs a rotor which includes permanent magnets in theinterior of the rotor, as a rotor of a brushless D.C. motor.

A brushless D.C. motor driving and controlling apparatus according toclaim 12 includes a phase controlling means for controlling voltage-fedinverters so that a phase of inverter output voltage is advanced from aphase of the inverter output voltage with respect to an induced voltageof a brushless D.C. motor, the latter phase being a phase which makes abrushless D.C. motor current and the induced voltage of the brushlessD.C. motor to be the same phase to one another.

A brushless D.C. motor driving and controlling apparatus according toclaim 13 includes a conducting interval determining means fordetermining a conducting interval of voltage-fed inverters to be 180° byelectrical angle.

A brushless D.C. motor driving and controlling apparatus according toclaim 14 further includes a difference voltage outputing means forreceiving a first voltage at a neutral point which is obtained by fromone end of resistors. Which are connected to each output terminal ofvoltage-fed inverters, a second voltage at a neutral point which isobtained from one end of stator windings of a brushless D.C. motor, andfor outputing a difference voltage between the first voltage and thesecond voltage, and a rotor position detecting means for detecting amagnetic pole position of a rotor of the brushless D.C. motor based uponthe difference voltage.

A brushless D.C. motor driving and controlling apparatus according toclaim 15 employs a conducting interval determining means for determininga conducting interval of voltage-fed inverters to be a predeterminedinterval which is more than 120° and less than 180° by electrical angle.

A brushless D.C. motor driving and controlling apparatus according toclaim 16 employs a conducting interval determining means for determininga conducting interval of voltage-fed inverters to be a predeterminedinterval which is equal or more than 140° and equal or less than 170° byelectrical angle.

Electrical equipment according to claim 17 employs a brushless D.C.motor as a driving source which motor is driven and controlled by one ofthe brushless D.C. motor driving and controlling apparatus according toclaims 9 through 16.

As to the brushless D.C. motor driving and controlling method accordingto claim 1, the method determines a conducting interval of voltage-fedinverters to be a predetermined interval which is more than 120° andequal or less than 180° by electrical angle when a brushless D.C. motoris driven by voltage-fed inverters. Therefore, the method determinesnon-control term to be less than 60° by electrical angle. As a result,the method increases motor terminal voltages and expands the operatingrange. Further, an increase of motor current is suppressed so that anincrease of joule losses due to motor windings are suppressed andefficiency of the brushless D.C. motor is improved, because the motorterminal voltages can be increased. Further, a current can be forciblyflowed in a desired direction in correspondence to an extent ofpermanent magnets which is installed to the rotor of the brushless D.C.motor, the extent being greater than 120° by electrical angle.Therefore, lowering of available rate of magnetic flux is suppressed andefficiency of the brushless D.C. motor is improved.

As to the brushless D.C. motor driving and controlling method accordingto claim 2, the method modulates outputs of voltage-fed inverters so asto output pulse signals, each pulse signal having constant pulse widthwithin an entire conducting interval. Therefore, magnetic pole positiondetection with high accuracy is not needed, and controlling issimplified. Also, the method improves efficiency and increases anamplitude of a fundamental wave in comparison to a case in whichvariable pulse width modulation is performed. The variable pulse widthmodulation varies pulse widthes of the pulse signal. Consequently, amaximum number of revolution of the brushless D.C. motor is increased.

As to the brushless D.C. motor driving and controlling method accordingto claim 3, the method employs a rotor which includes permanent magnetsin the interior of the rotor, as a rotor of a brushless D.C. motor.Therefore, the method generates not only a torque caused by the magnetbut also a torque caused by reluctance so that generated torque as awhole is increased without increasing motor currents. Further,inductance of motor windings is extremely increased in comparison tothat of a brushless D.C. motor in which permanent magnets are installedon a surface of a rotor, so that operating with higher speed can beachieved in comparison to that of the brushless D.C. motor in whichpermanent magnets are installed on the surface of the rotor.Furthermore, the method decreases a current ripple due to low orderhigher harmonics components of inverters, because inductance of motorwindings is great. Therefore, the method decreases a torque ripple.

As to the brushless D.C. motor driving and controlling method accordingto claim 4, the method controls voltage-fed inverters so that a phase ofinverter output voltage is advanced from a phase of the inverter outputvoltage with respect to an induced voltage of a brushless D.C. motor,the latter phase being a phase which makes a brushless D.C. motorcurrent and the induced voltage of the brushless D.C. motor to be thesame phase to one another. Therefore, influence of inductance in adirection which is shifted by 90° electrically from a direction ofmagnetic flux generated by a permanent magnet, is efficiently andpractically used. As a result, a current waveform is appoximated to be asine wave. Consequently, torque ripple is further reduced and motorefficiency is further improved. Furthermore, reluctance torque and fieldweakening effects are efficiently and practically utilized.

As to the brushless D.C. motor driving and controlling method accordingto claim 5, the method determines a conducting interval of voltage-fedinverters to be 180° by electrical angle. Therefore, a non-control termis determined to be 0° by electrical angle. Control of the conductinginterval within an extent which is smaller than 60°, is not necessary,because the conducting interval is 180°. Therefore, when the control isperformed using a microcomputer, a number of timers are decreased by 1and interrupt handlings are reduced by 1 in comparison to a case inwhich the conducting interval is determined to be greater than 120° andless than 180°. Consequently, the control and arrangement is simplified.When the control is performed using a hardware, a number oftimer-counter is decreased by 1 in comparison to a case in which theconducting interval is determined to be greater than 120° and less than180°. Consequently, the control and arrangement is simplified.

As to the brushless D.C. motor driving and controlling method accordingto claim 6, the method obtains a first voltage at a neutral point fromone end of resistors. Which are connected to each output terminal ofvoltage-fed inverters, obtains a second voltage at a neutral point fromone end of stator windings of a brushless D.C. motor, and detects amagnetic pole position of a rotor of the brushless D.C. motor based upona difference between the first voltage and the second voltage.Therefore, the magnetic pole position of the rotor is detected in spiteof the revolution speed, conducting angle, and amplitude of motorcurrent, without especially providing a sensor for detecting magneticpole position of the rotor.

As to the brushless D.C. motor driving and controlling method accordingto claim 7, the method determines a conducting interval of voltage-fedinverters to be a predetermined interval which is more than 120° andless than 180° by electrical angle. Therefore, the difference signalbetween the voltages and an integrated signal which is used to detectmagnetyic pole position of a motor rotor, is stabilized so thatreliability is improved.

As to the brushless D.C. motor driving and controlling method accordingto claim 8, the method determines a conducting interval of voltage-fedinverters to be a predetermined interval which is equal or more than140° and equal or less than 170° by electrical angle. Therefore, motorefficiency and operating range are scarcely detracted. And, thedifference signal between the voltages and an integrated signal isfurther stabilized so that reliability is further improved.

As to the brushless D.C. motor driving and controlling apparatusaccording to claim 9, when a brushless D.C. motor is driven byvoltage-fed inverters, the conducting interval determining meansdetermins a conducting interval of voltage-fed inverters to be apredetermined interval which is more than 120° and equal or less than180° by electrical angle. Therefore, the apparatus determines thenon-control term to be less than 60° by electrical angle. As a result,the apparatus increases motor terminal voltages and expands an operatingrange. Further, a quantity in increase of motor currents is suppressedso that an increase of joule losses due to motor windings is suppressedand efficiency of the brushless D.C. motor is improved, because themotor terminal voltages can be increased. Further, a current can beforcibly flowed in a desired direction in correspondence to an extent ofpermanent magnets which are installed onto the rotor of the brushlessD.C. motor, the extent being greater than 120° by electrical angle.Therefore, lowering of available rate of magnetic flux is suppressed andefficiency of the brushless D.C. motor is improved.

As to the brushless D.C. motor driving and controlling apparatusaccording to claim 10, the modulating means modulates outputs ofvoltage-fed inverters so as to output pulse signals, each pulse signalhaving constant pulse widths within an entire conducting interval.Therefore, magnetic pole position detection with high accuracy is notneeded, and controlling is simplified. Also, the apparatus improvesefficiency and increases an amplitude of a fundamental wave incomparison to a case in which variable pulse width modulation isperformed. The variable pulse width modulation varies pulse widths ofthe pulse signal. Consequently, a maximum number of revolution of thebrushless D.C. motor is increased.

As to the brushless D.C. motor driving and controlling apparatusaccording to claim 11, the apparatus employs a rotor which includespermanent magnets in the interior of the rotor, as a rotor of abrushless D.C. motor. Therefore, the apparatus generates not only atorque caused by the magnet but also a torque caused by reluctance sothat generated torque as a whole is increased without increasing motorcurrents. Further, inductance of motor windings is extremely increasedin comparison to that of a brushless D.C. motor in which permanentmagnets are installed on a surface of a rotor, so that higher speedoperating can be achieved in comparison to that of the brushless D.C.motor in which permanent magnets are installed on the surface of therotor. Furthermore, the apparatus decreases a current ripple due to loworder higher harmonics components of inverters, because inductance ofmotor windings is great. Therefore, the apparatus decreases a torqueripple.

As to the brushless D.C. motor driving and controlling apparatusaccording to claim 12, the phase controlling means controls voltage-fedinverters so that a phase of inverter output voltage is advanced from aphase of the inverter output voltage with respect to an induced voltageof a brushless D.C. motor, the latter phase being a phase which makes abrushless D.C. motor current and the induced voltage of the brushlessD.C. motor to be the same phase to one another. Therefore, influence ofinductance in a direction which is shifted by 90° electrically from adirection of magnetic flux generated by a permanent magnet, isefficiently and practically utilized. As a result, a current waveform isappoximated to be a sine wave. Consequently, torque ripple is furtherreduced and motor efficiency is further improved. Furthermore,reluctance torque and field weakening effects are efficiently andpractically utilized.

As to the brushless D.C. motor driving and controlling apparatusaccording to claim 13, the conducting interval determining meansdetermins a conducting interval of voltage-fed inverters to be 180° byelectrical angle. Therefore, a non-control term is determined to be 0°by electrical angle. Control of the conducting interval within an extentwhich is smaller than 60°, is not necessary, because the conductinginterval is 180°. Therefore, when the control is performed using amicrocomputer, a number of timers is decreased by 1 and interrupthandlings are reduced by 1 in comparison to a case in which theconducting interval is determined to be greater than 120° and less than180°. Consequently, the control and arrangement is simplified. When thecontrol is performed using hardware, a number of timer-counter isdecreased by 1 in comparison to a case in which the conducting intervalis determined to be greater than 120° and less than 180°. Consequently,the control and arrangement is simplified.

As to the brushless D.C. motor driving and controlling apparatusaccording to claim 14, the apparatus obtains a first voltage at aneutral point from resistors which are connected at one end to oneanother and are connected at their other ends to each output terminal ofvoltage-fed inverters, obtains a second voltage at a neutral point whichis obtained at the connected ends of stator windings of a brushless D.C.motor which windings are connected to one another, and the differencevoltage outputing means outputs a difference voltage between the firstvoltage and the second voltage, and the rotor position detecting meansdetects a magnetic pole position of a rotor of the brushless D.C. motorbased upon the difference voltage. Therefore, the magnetic pole positionof the rotor is detected in spite of the revolution speed, conductingangle, and amplitude of motor current, without especially providing asensor for detecting magnetic pole position of the rotor.

As to the brushless D.C. motor driving and controlling apparatusaccording to claim 15, the apparatus employs a conducting intervaldetermining means for determining a conducting interval of voltage-fedinverters to be a predetermined interval which is more than 120° andless than 180° by electrical angle. Therefore, the difference signalbetween the voltages a an integrated signal which is used to detectmagnetic pole position of a motor rotor, is stabilized so thatreliability is improved.

As to the brushless D.C. motor driving and controlling apparatusaccording to claim 16, the apparatus employs a conducting intervaldetermining means for determining a conducting interval of voltage-fedinverters to be a predetermined interval which is equal or more than140° and equal or less than 170° by electrical angle. Therefore, motorefficiency and operating range are scarcely detracted. And, thedifference signal between the voltages or an integrated signal isfurther stabilized so that reliability is further improved.

As to the electrical equipment according to claim 17, the equipmentemploys a brushless D.C. motor as a driving source which motor is drivenand controlled by one of the brushless D.C. motor driving andcontrolling apparatus according to claims 9 through 16. Therefore,reduced power consumption is achieved due to the improvement of higherefficiency of a brushless D.C. motor which is the driving source.

The present invention is described in more detail.

When a brushless D.C. motor is driven by voltage-fed inverters whichhave a conducting interval of 120° by electrical angle, ideal currentwaveforms and an ideally generated torque are illustrated in FIGS. 1(A)through 1(D). A brushless D.C. motor is a motor which replacesmechanical commutators of a d.c. motor with inverters. Therefore, wheninverters are controlled so that each current of three phases (U, V, W)is joined at every 120° so as to make a motor current to be a directcurrent, a generated torque becomes similar to that of a d.c. motor, asis illustrated in FIG. 1(D).

A simulation result is illustrated in FIGS. 2(A) and 2(B) whichsimulation is carried out by the inventors of the present invention andis carried out for a current waveform and generated torque when abrushless D.C. motor is driven by voltage-fed inverters which has aconducting interval of 180° by electrical angle. In this case, portionsare generated in which a current of each phase overlaps one another sothat the brushless D.C. motor performs an operation which is differentfrom that of a d.c. motor, because currents flow for a 180° term. As aresult, ripple in the generated torque becomes great {refer to FIG.2(B)}.

From the above point of view, it is conventionally thought thatvoltage-fed inverters which has a conducting interval of 120° byelectrical angle, is ideal for driving a brushless D.C. motor.Therefore, only a method which employs a conducting interval of 120° byelectrical angle, is proposed and is available as a driving method of abrushless D.C. motor which driving method uses magnetic pole positiondetection based upon detection of induced voltages of a motor. But, whenthe inventors drives a brushless D.C. motor using voltage-fed inverterswhich has a conducting interval of 120° by electrical angle, theinventors have found that ideal waveforms illustrated in FIGS. 1 are notobtained, and that waveforms illustrated in FIGS. 3(A) and 3(B) areobtained, and that the waveforms illustrated in FIGS. 3(A) and 3(B) aresimilar to the waveforms illustrated in FIGS. 2(A) and 2(B). When FIG.2(B) and FIG. 3(B) are compared to one another, it is understood thatamplitudes of both torque ripple are in nearly the same degree to oneanother. It seems the reason that motor current cannot be controlled ina desired manner (controlled to be a rectangular waveform) whenvoltage-fed inverters employs a simple control is employed. Therefore,it becomes clear that lowering in efficiency and decreasing in operatingrange are not realized, the lowering and the decreasing beingapprehended when a brushless D.C. motor is driven with a conductinginterval of 180° by electrical angle. Rather, it becomes clear thatefficiency of a brushless D.C. motor is improved by reduction of joulelosses and depression of lowering in flux available rate.

Further, when voltage-fed inverters which has a conducting intervalexceeding 120° (other than 180°), portions are inevitably generated inwhich a current of each phase overlaps one another so that a characterseems to be obtained which is similar to that of voltage-fed inverterswith a conducting interval of 180° by electrical angle.

Furthermore, in the voltage-fed inverters with a conducting interval of120° by electrical angle, the character is improved by approximatingeach current waveform to a rectangular wave, as is illustrated in FIGS.1(A) through 1(C). On the contrary, in the voltage-fed inverters with aconducting interval of 180° by electrical angle, the character seems tobe improved by smoothing each current waveform because each currentflows in the entire interval.

The present invention was made based upon the above findings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 are diagrams illustrating ideal current waveforms and generatedtorque for a brushless D.C. motor driven by voltage-fed inverters with aconducting interval of 120° by electrical angle;

FIGS. 2 are diagrams illustrating simulation results of a currentwaveform and generated torque for a brushless D.C. motor driven byvoltage-fed inverters with a conducting interval of 180° by electricalangle;

FIGS. 3 are diagrams illustrating a current waveform and generatedtorque for a brushless D.C. motor driven by voltage-fed inverters with aconducting interval of 120° by electrical angle;

FIG. 4 is a schematic block diagram illustrating an embodiment of abrushless D.C. motor driving and controlling apparatus according to thepresent invention;

FIG. 5 is a schematic cross sectional view of a brushless D.C. motor inwhich permanent magnets are installed on a surface of a rotor;

FIG. 6 is a schematic cross sectional view of a brushless D.C. motor inwhich permanent magnets are installed interior of a rotor;

FIGS. 7 are graphs illustrating efficiency-revolution numbercharacteristics and load torque-revolution number characteristics when abrushless D.C. motor having an arrangement illustrated in FIG. 5 isdriven by voltage-fed inverters, and a conducting interval is determinedto be 120°, 180° by electrical angle, respectively;

FIGS. 8 are graphs illustrating efficiency-revolution numbercharacteristics and load torque-revolution number characteristics when abrushless D.C. motor having an arrangement illustrated in FIG. 6 isdriven by voltage-fed inverters, and a conducting interval is determinedto be 120°, 150°, 180° by electrical angle, respectively;

FIGS. 9 are graphs illustrating efficiency-revolution numbercharacteristics and load torque-revolution number characteristics when abrushless D.C. motor having an arrangement illustrated in FIG. 6 isdriven by voltage-fed inverters, and the inverter is modulated in aconstant pulse width manner and variable pulse width manner,respectively by control circuitry;

FIGS. 10 are diagrams illustrating constant pulse width modulation andvariable pulse width modulation;

FIGS. 11 are diagrams illustrating a voltage waveform and currentwaveform when a brushless D.C. motor in which permanent magnets areinstalled on a surface of a rotor, is driven by voltage-fed inverterswith a conducting interval of 180° by electrical angle and outputtingconstant pulse width modulation waveform;

FIGS. 12 are diagrams illustrating a voltage waveform and currentwaveform when a brushless D.C. motor in which permanent magnets areinstalled interior of a rotor, is driven by voltage-fed inverters with aconducting interval of 180° by electrical angle and outputting constantpulse width modulation waveform;

FIGS. 13 are diagrams illustrating a voltage waveform and a currentwaveform when a brushless D.C. motor in which permanent magnets areinstalled in the interior of a rotor, is supplied inverter outputvoltages which is advanced in phase from a phase which makes a phase ofa brushless D.C. motor current and a phase of induced voltage of thebrushless D.C. motor equal to one another;

FIG. 14 is a diagram schematically illustrating a brushless D.C. motordriving and controlling apparatus which achieves a conducting intervalof 180° by electrical angle;

FIG. 15 is a diagram illustrating an inner arrangement of amicroprocessor which is illustrated in FIG. 14;

FIG. 16 is a flowchart which explains processing contents of aninterrupt handling 1 in detail;

FIG. 17 is a flowchart which explains processing contents of aninterrupt handling 2 in detail;

FIGS. 18 are diagrams illustrating signal waveforms and processingcontents of each section of the brushless D.C. motor driving andcontrolling apparatus which is illustrated in FIG. 14;

FIG. 19 is a block diagram illustrating an inner arrangement of amicroprocessor which is incorporated in a brushless D.C. motor drivingand controlling apparatus which achieves a conducting interval of 150°by electrical angle;

FIG. 20 is a flowchart which explains processing contents of aninterrupt handling 2' in detail;

FIG. 21 is a flowchart which explains processing contents of aninterrupt handling 3 in detail;

FIGS. 22 are diagrams illustrating signal waveforms and processingcontents of each section of the brushless D.C. motor driving andcontrolling apparatus which is illustrated in FIG. 19;

FIGS. 23 are diagrams illustrating signal waveforms of each section ofthe brushless D.C. motor driving and controlling apparatus which isillustrated in FIG. 14, which diagrams are useful in understandingposition detection operation by an amplifier, integrator and zero-crosscomparator;

FIGS. 24 are diagrams illustrating a motor current and an integrationsignal of a position detector when a conducting interval of 180° byelectrical angle, is employed;

FIGS. 25 are diagrams illustrating a motor current and an integrationsignal of a position detector when a conducting interval of 120° byelectrical angle, is employed;

FIGS. 26 are diagrams illustrating a motor current and an integrationsignal of a position detector when a conducting interval of 130° byelectrical angle, is employed;

FIGS. 27 are diagrams illustrating a motor current and an integrationsignal of a position detector when a conducting interval of 140° byelectrical angle, is employed;

FIGS. 28 are diagrams illustrating a motor current and an integrationsignal of a position detector when a conducting interval of 150° byelectrical angle, is employed;

FIGS. 29 are diagrams illustrating a motor current and an integrationsignal of a position detector when a conducting interval of 160° byelectrical angle, is employed;

FIGS. 30 are diagrams illustrating a motor current and an integrationsignal of a position detector when a conducting interval of 170° byelectrical angle, is employed;

FIG. 31 is a diagram illustrating operating ranges of a brushless D.C.motor when a conducting interval is determined to be 120°, 130°, 140°,150°, 180° by electrical angle, respectively, and input currents aredetermined to be the same; and

FIG. 32 is a diagram illustrating motor efficiencies of a brushless D.C.motor when a conducting interval is determined to be 120°, 130°, 140°,150°, 180° by electrical angle, respectively, and input currents aredetermined to be the same to one another.

BEST MODE FOR IMPLEMENTING THE INVENTION

Hereinafter, referring to the attached drawings, we explain the presentinvention in detal.

FIG. 4 is a schematic block diagram illustrating an embodiment of abrushless D.C. motor driving and controlling apparatus according to thepresent invention. Output voltages of inverters 2 are supplied to abrushless D.C. motor 3. A second voltage at a neutral point is obtainedby Y-connecting induced voltages of the brushless D.C. motor 3 or byY-connecting stator windings of each phase of the brushless D.C. motor3. A first voltage at a neutral point is obtained by Y-connectingresistors between output terminals of each phase of the inverters 2. Amotor position detection circuitry 4 receives a difference voltagebetween the first voltage and the second voltage. An output signal fromthe motor position detection circuitry 4 is supplied to a controlcircuitry 5. The control circuitry 5 generates a control command fordetermining a conducting interval to be more than 120° and equal to orless than 180° by electrical angle, and supplies the control command tothe inverters 2. When the control circuitry 5 generates a controlcommand for determining the conducting interval to be equal to 180° byelectrical angle and supplies the control command to the inverters 2,the difference voltage should be supplied to the motor positiondetection circuitry 4. But when the control circuitry 5 generates acontrol command for determining the conducting interval to be less than180° by electrical angle and supplies the control command to theinverters 2, the induced voltages or difference voltage may be suppliedto the motor position detection circuitry 4.

Therefore, a detection signal corresponding to a magnetic pole positionof a motor rotor is obtained by the motor position detection circuitry 4based upon the induced voltages of the brushless D.C. motor 3 or thedifference voltage between the first and second voltages. The controlcircuitry 5 generates the control command based upon the magnetic poleposition detection signal. The control command controls switches (notillustrated) the inverters 2 so that the conducting interval isdetermined to be more than 120° by electrical angle and equal to or lessthan 180° by electrical angle.

FIG. 5 is a schematic cross sectional view of a brushless D.C. motor inwhich permanent magnets are installed on a surface of a rotor. Permanentmagnets 3b are installed at predetermined position on a surface of arotor 3a. A stator 3c includes a plurality of slots 3d in which statorwindings (not illustrated) are wound. A d-axis which is indicated by anarrow in FIG. 5, is an axis indicating a direction of magnetic fluxgenerated by the permanent magnet 3b. A q-axis is an axis which isshifted 90° electrically with respect to the d-axis.

FIG. 6 is a schematic cross sectional view of a brushless D.C. motor inwhich permanent magnets are installed interior of a rotor. Permanentmagnets 3f are installed such that they are not exposed. Non-magneticbodies 3g are installed between neighbouring permanent magnets 3f sothat short-magnetic circuit between the neighbouring permanent magnets3f is prevented from occurrence. An arrangement of a stator 3c issimilar to that of the brushless D.C. motor illustrated in FIG. 5,therefore decription is omitted.

FIGS. 7(A) and 7(B) are graphs illustrating efficiency-revolution numbercharacteristics and load torque-revolution number characteristics when abrushless D.C. motor having an arrangement illustrated in FIG. 5 isdriven by voltage-fed inverters, and a conducting interval is determinedto be 120°, 180° by electrical angle, respectively. In FIG. 7(A), thecharacteristics are obtained under a condition that load torque isdetermined to be 20 kg·cm. Also, in the figures, a representscharacteristics when a conducting interval is determined to be 120° byelectrical angle, and b represents characteristics when a conductinginterval is determined to be 180° by electrical angle.

As is apparent from these figures, efficiency is improved, a maximumrevolution number is raised, and load torque in a high revolution rangeis increased, by determining the conducting interval to be 180° byelectrical angle.

FIGS. 8(A) and 8(B) are graphs illustrating efficiency-revolution numbercharacteristics and load torque-revolution number characteristics when abrushless D.C. motor having an arrangement illustrated in FIG. 6 isdriven by voltage-fed inverters, and a conducting interval is determinedto be 120°, 150°, 180° by electrical angle, respectively. In FIG. 8(A),characteristics are obtained under a condition that load torque isdetermined to be 20 kg·cm. Also, in the figures, a representscharacteristics when a conducting interval is determined to be 120° byelectrical angle, b represents characteristics when a conductinginterval is determined to be 150° by electrical angle, and c representscharacteristics when a conducting interval is determined to be 180° byelectrical angle.

As is apparent from these figures, efficiency is improved, a maximumrevolution number is raised, and load torque in a high revolution rangeis increased, when the conducting interval is high.

FIGS. 9(A) nd 9(B) are graphs illustrating efficiency-revolution numbercharacteristics and load torque-revolution number characteristics when abrushless D.C. motor having an arrangement illustrated in FIG. 6 isdriven by voltage-fed inverters, and the inverters are modulated in aconstant pulse width manner and variable pulse width manner,respectively by control circuitry. In FIG. 9(A), characteristics areobtained under a condition that load torque is determined to be 20 kg·cmand a conducting interval is determined to be 180° by electrical angle.Also, in the figures, a represents characteristics when variable pulsewidth modulation is performed, and b represents characteristics whenconstant pulse width modulation is performed.

The variable pulse width modulation is a method for obtaining a voltagewaveform which is equivalent to a sine wave and the like, by varyingpulse widthes, as is illustrated in FIG. 10(A). The constant pulse widthmodulation is a method which does not vary pulse widths at all, as isillustrated in FIG. 10(B).

As is apparent from these characteristics figures, efficiency isimproved, a maximum revolution number is raised, and load torque in ahigh revolution range is increased, by employing the constant pulsewidth modulation.

Hereinafter, description is made in more detail.

A pulse width modulation method which employs variable pulse widths suchas sine wave modulation, is generally employed in other driving andcontrolling methods for motors and the like, because it is thought thatlow order higher harmonics waves cause increase in losses and vibration(refer to "Frequency Dependency of Induction Motor Parameters and TheirMeasuring Method", K.Kawagishi et. al., IPEC-Tokyo'83,pp.202-213,1983).When the method is applied to a brushless D.C. motor, a magnetic poledetection means with high accuracy is needed and control becomescomplicated so that a cost as a whole is increased because a modulationsignal waveform and a rotor should be synchronized to one another. But,the constant pulse width modulation does not have such disadvantages,and has an amplitude of a fundamental wave which is higher than that ofa fundamental wave of variable pulse width modulation. Further, as isapparent from FIGS. 9 which represent the inventors' knowledge, loweringefficiency was not recognized, instead efficiency was improved.Furthermore, vibration was almost inconsiderable when the method wastaken in an air conditioner and the like.

Next, a brushless D.C. motor in which permanent magnets are installed ona surface of a rotor, and a brushless D.C. motor in which permanentmagnets are installed in the interior of a rotor, are describedcontradistinctionally in detail (refer to FIGS. 5 and 6).

The brushless D.C. motor in which permanent magnets are installed on asurface of a rotor, which motor is illustrated in FIG. 5, includespermanent magnets 3b which are disposed on a surface of silicon steelplates of the rotor 3a. Therefore, an air gap (a distance betweensilicon steel plates of the rotor and silicon steel plates of a stator)is great so that inductance of-stator windings become comparativelysmall. On the contrary, the brushless D.C. motor in which permanentmagnets are installed interior of the rotor, which motor is illustratedin FIG. 6, includes permanent magnets 3b which are disposed interior ofsilicon steel plates of the rotor 3a. Therefore, an air gap is small sothat inductance of stator windings become extremely great in comparisonto that of the brushless D.C. motor in which permanent magnets areinstalled on the surface of the rotor, because the permanent magnets areinstalled interior of the rotor 3e.

FIGS. 11 and 12 are diagrams illustrating a voltage waveform and currentwaveform when a brushless D.C. motor in which permanent magnets areinstalled on a surface of a rotor and a brushless D.C. motor in whichpermanent magnets are installed on the interior of a rotor, is driven,respectively, by voltage-fed inverters with a conducting interval of180° by electrical angle and outputting constant pulse width modulationwaveform. In both figures, voltage waveforms are illustrated in upperportions, while current waveforms are illustrated in lower portions.

As is apparent from both figures, due to effects of inductance of statorwindings, a motor current becomes similar to a sine wave when abrushless D.C. motor in which permanent magnets are installed on theinterior of a rotor, is employed, so that losses caused by higherharmonic currents are reduced and efficiency is improved. Further,torque ripple is reduced.

A brushless D.C. motor in which permanent magnets are installed on asurface of a rotor, and a brushless D.C. motor in which permanentmagnets are installed interior of a rotor, are further describedcontradistinctionally in deteil.

The brushless D.C. motor in which permanent magnets are installed on asurface of a rotor, which motor is illustrated in FIG. 5, hascylindrical shaped silicon steel plates which constitute a rotor 3a.Therefore, inductance of stator windings are maintained to be constantregardless of rotational position of the rotor 3a. On the contrary, thebrushless D.C. motor in which permanent magnets are installed on theinterior of a rotor 3e, which motor is illustrated in FIG. 6, hassilicon steel plates which are magnetic bodies, and non-magnetic bodies3g, which silicon steel plates and non-magnetic bodies 3g arealternately disposed in a portion of the rotor 3e which portion is closeto an outer periphery of the rotor 3e. Therefore, inductance of statorwindings vary depending upon rotational position of the rotor 3e.Specifically, when the brushless D.C. motor in which permanent magnetsare installed on the surface of the rotor, and the brushless D.C. motorin which permanent magnets are installed interior of the rotor, areoperated in nominal conditions, both d-axis inductance and q-axisinductance of the former brushless D.C. motor are 3.2 mH, while d-axisinductance and q-axis inductance of the latter brushless D.C. motor are7.7 mH, 22.8 mH, respectively.

A method for outputting inverter voltages which maximize a d-axisvoltage (induced voltage of the motor), that is for outputting invertervoltages so that a phase of a motor current and a phase of the inducedvoltage of the motor are the same to one another, is generally employedas a driving and controlling method of a brushless D.C. motor, becausemagnetic flux of permanent magnets are intended to be available at itsmaximum. In FIGS. 11, a phase of inverter voltage is advanced by 29°with respect to a phase of induced voltage of a brushless D.C. motor inwhich permanent magnets are installed on a surface of a rotor. FIGS. 11are obtained under a condition that a number of revolutions 2858 r.p.m.,load torque is 20 kg·cm, a motor voltage is 114.0 V, and a motor currentis 7.20 A. In FIGS. 11, scales are 200 V/div. for voltage, 10 A/div. forcurrent, and 2 msec/div. for horizontal axis. Further, the advancedangle varies depending upon motor constants.

But, a brushless D.C. motor in which permanent magnets are installedinterior of a rotor, has inductance of stator windings which is slightlygreater than that of the former brushless D.C. motor. Therefore, acurrent waveform becomes a waveform which is illustrated in FIGS. 12.FIGS. 12 are obtained under conditions that a number of revolutions is2858 r.p.m., load torque is 20 kg·cm, a motor voltage is 126.5 V, and amotor current is 5.76 A. In FIGS. 12, scales are 200 V/div. for voltage,10 A/div. for current, and 2 msec/div. for horizontal axis. A phase ofinverter voltage is advanced by 70° with respect to a phase of aninduced voltage of the motor in a case which is illustrated in FIG. 12.The advanced angle varies depending upon motor constants. When a phaseof inverter voltage is further advanced with respect to the above phaseof inverter voltage (advanced angle is 73°), and the inverter voltage issupplied to the brushless D.C. motor, a current waveform illustrated inlower portion of FIGS. 13 is obtained. FIGS. 13 are obtained underconditions that a number of revolutions is 2858 r.p.m., load torque is20 kg·cm, a motor voltage is 89.6 V, and a motor current is 6.92 A. InFIGS. 13, scales are 200 V/div. for voltage, 10 A/div. for current, and2 msec/div. for horizontal axis. A voltage waveform is illustrated inupper portion of FIGS. 13.

When FIGS. 12 and 13 are compared to one another, it is understood thatthe current waveform is quite similar to a sine wave due to the effectof q-axis inductance. Therefore, torque ripple reducing effect andefficiency improving effect are further improved. Further, "reluctancetorque" and "field weakening effect" which are other characteristics ofa brushless D.C. motor in which permanent magnets are installed interiorof a rotor, are effectively utilized.

FIG. 14 is a diagram schematically illustrating a brushless D.C. motordriving and controlling apparatus which achieves a conducting intervalof 180° by electrical angle, while FIG. 15 is a diagram illustrating aninner arrangement of a microprocessor which is illustrated in FIG. 14.Three pairs of switching transistors 12u1, 12u2, 12v1, 12v2, 12w1, 12w2are serially connected, respectively, between terminals of a d.c. powersource 11 so that inverters 12 are constituted. A voltage at eachconnecting point of each pair of switching transistors is supplied toeach of three stator windings 13u, 13v, 13w of a brushless D.C. motor13, the stator windings 13u, 13v, 13w being Y-connected and each of thestator windings 13u, 13v, 13w corresponding to each phase. Also, avoltage at each connecting point of each pair of switching transistorsis supplied to each of three resistors 14u, 14v, 14w which areY-connected. Further, diodes 12u1d, 12u2d, 12v1d, 12v2d, 12w1d, 12w2dfor protection are connected between collector-emitter terminals of theswitching transistors 12u1, 12u2, 12v1, 12v2, 12w1, 12w2, respectively.Furthermore, 13e represents a rotor of the brushless D.C. motor 13.Suffixes of u, v, w correspond to u-phase, v-phase, w-phase of thebrushless D.C. motor 13, respectively. A second voltage of a neutralpoint 13d of the Y-connected stator windings 13u, 13v, 13w is suppliedto a reversed input terminal of an amplifier 15 through a resistor 15a.A first voltage of a neutral point 14d of the Y-connected resistors 14u,14v, 14w is supplied as it is to a non-reversed input terminal of theamplifier 15. A resistor 15b is connected between an output terminal andthe reversed input terminal of the amplifier 15 so that the amplifier 15operates as an differential amplifier.

An output signal output from the outputed terminal of the amplifier 15is supplied to an integrator 16 which is constituted by seriallyconnecting a resistor 16a and a capacitor 16b.

An output signal from the integrator 16 (a voltage at a connecting pointof the resistor 16a and the capacitor 16b) is supplied to a non-reversedinput terminal of a zero-cross comparator 17 which is supplied thesecond voltage of the neutral point 13d to its reversed input terminal.

Therefore, a magnetic pole position detection signal is output from anoutput terminal of the zero-cross comparator 17. In other words, aposition detector is constituted by the differential amplifier,integrator 16 and zero-cross comparator 17. A position detector which isconstituted by a rotary encoder and the like may be employed instead ofthe position detector having the above arrangement.

The magnetic pole position detection signal output from the positiondetector is supplied to an external interruption terminal of amicroprocessor 18. In the microprocessor 18, an interrupt handling(refer to interrupt handling 1 in FIG. 15) for a phase correction timer18a and a period measurement timer 18b, is carried out based upon themagnetic pole position detection signal which is supplied to theexternal interruption terminal. The phase correction timer 18adetermines its timer value by a timer value operating section 19a whichis described later. The period measurement timer 18b supplies its timervalue to a position signal period operating section 19b which isincluded in a CPU 19. The position signal period operating section 19bcalculates a timer value per 1 cycle by electrical angle based upon atimer value corresponding to 60° by electrical angle, for example. Thephase correction timer 18a supplies a count - - - over signal toinverter mode selection section 19c for a conducting interval of 180° byelectrical angle so that an interrupt handling (refer to an interrupthandling 2 in FIG. 2) is carried out. The inverter mode selectionsection 19c for a conducting interval of 180° by electrical angle, readsout corresponding voltage pattern from a memory 18c and outputstherefrom. In the CPU 19, the position signal period operating section19b performs operations based upon the timer value and outputs aposition signal period signal which is supplied to a timer valueoperating section 19a and a velocity operating section 19e. The timervalue operating section 19a is also supplied a phase angle command. Thetimer value operating section 19a calculates timer value which isdetermined in the phase correction timer 18a, based upon the phase anglecommand and the position signal period signal from the position signalperiod operating section 19b. The velocity operating section 19ecalculates a velocity at the present time based upon the position signalperiod signal from the position signal period operating section 19b, andsupplies the calculated velocity to a velocity controlling section 19f.The velocity controlling section 19f is also supplied a velocitycommand. The velocity controlling section 19f outputs a voltage commandbased upon the velocity command and the velocity at the present timefrom the velocity operating section 19e. And, the voltage pattern outputfrom the inverter mode selection section 19c for a conducting intervalof 180° by electrical angle, and the voltage command output from thevelocity controlling section 19f are supplied to a PWM (Pulse WidthModulation) modulation section 18d. The PWM modulation section 18doutputs PWM modulation signals for three phases. The PWM modulationsignals are supplied to a base driving circuitry 20. The base drivingcircuitry 20 outputs control signals for supplying base terminals of theswitching transistors 12u1, 12u2, 12v1, 12v2, 12w1, 12w2. Each sectionincluded in the CPU 19 represents a functional portion for performing acorresponding function. These sections do not exist in the CPU 19 in arecognizable condition.

The Voltage patterns corresponding to inverter modes are represented intable 1. The voltage patterns are represented with ON-OFF conditions ofthe switching transistors 12u1, 12u2, 12v1, 12v2, 12w1, 12w2. "1"corresponds to ON condition, while "0" corresponds to OFF condition.

                  TABLE 1                                                         ______________________________________                                        Inverter Voltage-Fed inverters                                                mode     12u1   12u2     12v1 12v2   12w1 12w2                                ______________________________________                                        0        1      0        0    1      1    0                                   1        1      0        0    1      0    1                                   2        1      0        1    0      0    1                                   3        0      1        1    0      0    1                                   4        0      1        1    0      1    0                                   5        0      1        0    1      1    0                                   ______________________________________                                    

Next, referring to waveform diagrams illustrated in FIGS. 18, operationof the brushless D.C. motor driving and controlling apparatus which isillustrated in FIG. 14, is described.

The u-phase, v-phase and w-phase induced voltages Eu, Ev, Ew of thebrushless D.C. motor vary under a condition that three induced voltagesare sequentially shifting their phase by 120°, as is illustrated inFIGS. 18(A), 18(B) and 18(C). The signal Vnm output from the amplifier15 varies, as is illustrated in FIG. 18(D). An integration waveform(formula (1)) which is obtained by performing integration of the signalVnm by the integrator 16, varies, as is illustrated in FIG. 18(E).

    ∫Vnmd t                                               (1)

The integration waveform is supplied to the zero-cross comparator 17,and the zero-cross comparator 17 outputs a exitation change-over signalwhich rises or falls at zero-cross points of the integration signal, asis illustrated in FIG. 18(F). The interrupt handling 1 is performed dueto the rising and falling of the excitation change-over signal so thatthe phase correction timer 18a starts {refer to start points of arrowsillustrated in FIG. 18(G)}. The phase correction timer 18a performs timecounting operation for the determined timer value and count-over isgenerated {refer to end points of arrows illustrated in FIG. 18(G)},because the phase correction timer 18a is determined its timer value bythe timer value operating section 19b. The interrupt handling 2 iscarried out at every generation of count-over of the phase correctiontimer 18a, and the inverter mode selection section 19c for a conductinginterval of 180° by electrical angle, advances the inverter mode by 1step. That is, the inverter mode is selected in the order of "1", "2","3", "4", "5", "0", "1", "2", . . . , as is illustrated in FIG. 18(N).The inverter mode is advanced by 1 step due to the count-over of thephase correction timer 18a, so that the switching transistors 12u1,12u2, 12v1, 12v2, 12w1, 12w2 ON-OFF conditions are controlled incorrespondence to each inverter mode, as are illustrated in FIGS. 18(H)through 18(M). As a result, driving of the brushless D.C. motor 13 isperformed under a condition that the conducting term is determined to be180° by electrical angle, and the phase of the inverter voltage isdetermined to be an advanced phase with respect to the induced voltageof the motor. Wherein, an advancing angle of the phase of the invertervoltage is controlled by the phase correction timer 18a.

FIG. 16 is a flowchart which explains the processing of the interrupthandling 1 in detail. An external interruption request is accepted at arising edge and falling edge, respectively, of a magnetic pole positiondetection signal (which signal corresponds to the exitation change-oversignal) of the position detector. In step SP1, a timer value of thephase correction timer 18a is calculated based upon an externallysupplied phase angle (phase correction angle) command and the positionsignal period signal obtained by the position signal period operatingsection 19b. In step SP2, the phase correction timer 18a is set with acorrection timer value (timer value for correction). In step SP3, thephase correction timer 18a is started. In step SP4, the periodmeasurement timer 18b is stopped which was started in the previousinterrupt handling 1. In step SP5, The timer value of the periodmeasurement timer 18b is stored. These processings in steps SP4 and SP5are processings for detecting a period of an edge of the exitationchange-over signal. Therefore, the period measurement timer 18b is resetand started immediately after the reading of the timer value of theperiod measurement timer 18b, for the next period measurement. In stepSP6, an operation of the stored position signal period (for example,calculation of a counting number per 1° by electrical angle). In stepSP7, the revolution number at the present time of the brushless D.C.motor 13 is calculated based upon the position signal period operationresult. In step SP8, velocity controlling is performed following theexternally supplied velocity command, and the voltage command is output.Thereafter, processing is returned to prior processing.

Specifically, when the count value corresponding to the interval of themagnetic pole position detection signal is 360, obtained by actualmeasurement by the period measurement timer 18b, the count value per 1period of the inverter output voltage becomes 360×6=2160 because anumber of inverter modes is 6. And, the count value for 1° becomes2160/360=6 because the count value of 2160 corresponds to 360°. When thephase angle command is 60°, the count value (timer value) correspondingto the phase angle command becomes 6×60=360. Therefore, the value of 360is set in the phase correction timer 18a as the timer value forcorrection, and the phase correction timer 18a is started.

FIG. 17 is a flowchart which explains contents processing of theinterrupt handling 2 in detail. The interrupt handling 2 is acceptedwhen the phase correction timer 18a started in the interrupt handling 1,becomes count-over condition. In step SP1, the inverter mode, previouslydetermined in the memory 18c, is advanced by 1 step which inverter modeis. In step SP2, the voltage pattern corresponding to the advancedinverter mode is output. Thereafter, processing is returned to priorprocessing.

Therefore, a number of timers is decreased by 1 and interrupt handlingsare decreased by 1 when the above controlling is realized using amicrocomputer, which advantages will be apparent by comparing the aboveembodiment to a comparative example which is described below. Further,when the above contolling is realized using hardware, a number ofcounters is decreased by 1.

COMPARATIVE EXAMPLE

FIG. 19 is a diagram illustrating an inner arrangement of themicroprocessor 18 which is incorporated in a brushless D.C. motordriving and controlling apparatus for realizing a conducting interval of150° by electrical angle. The microprocessor 18 realizes the conductinginterval of 150° by electrical angle. The inner arrangement differs fromthe inner arrangement which is illustrated in FIG. 15 in that aninverter mode selection section 19c' for a conducting interval of 150°by electrical angle, is employed instead of the inverter mode selectionsection 19c for a conducting interval of 180° by electrical angle, asecond phase correction timer 18e is further provided, and contents ofthe interrupt handling 2' and a number of inverter modes are increased.The second phase correction timer 18e is started in the interrupthandling 2' which is caused by the phase correction timer 18a', andsupplies its count-over signal to the inverter mode selection section19c', included in the CPU 19' for a conducting interval of 150° byelectrical angle so that an interrupt handling (refer to the interrupthandling 3 in FIG. 19) is carried out. In this comparative example,component sections corresponding to the component sections illustratedin FIG. 15, have reference numerals with "/" added. Further,arrangements and interconnections of the inverter circuitry, brushlessD.C. motor, Y-connected resistors, position detector, base drivingcircuitry are the same to the arrangements and interconnectionsillustrated in FIG. 14, therefore illustration and description areomitted.

The second phase correction timer 18e determines its timer value by thetimer value operating section 19a'.

Voltage patterns corresponding to inverter modes are represented intable 2. The voltage patterns are represented with ON-OFF conditions ofthe switching transistors 12u1, 12u2, 12v1, 12v2, 12w, 12w2. And, "1"corresponds to ON condition, while "0" corresponds to OFF condition.

                  TABLE 2                                                         ______________________________________                                        Inverter Voltage-Fed inverters                                                mode     12u1   12u2     12v1 12v2   12w1 12w2                                ______________________________________                                        0        1      0        0    1      1    0                                   1        1      0        0    1      0    0                                   2        1      0        0    1      0    1                                   3        1      0        0    0      0    1                                   4        1      0        1    0      0    1                                   5        0      0        1    0      0    1                                   6        0      1        1    0      0    1                                   7        0      1        1    0      0    0                                   8        0      1        1    0      1    0                                   9        0      1        0    0      1    0                                   10       0      1        0    1      1    0                                   11       0      0        0    1      1    0                                   ______________________________________                                    

FIGS. 22 are waveform diagrams of component sections. There waveformsrepresent the operation of this comparative example. Waveformsillustrated in FIGS. 22(A) through 22(G) are the same to those of FIGS.18(A) through 18(G). And, voltage patterns corresponding to invertermodes which correspond to even numbers, are outputed by the interrupthandling 2' and voltage patterns corresponding to inverter modes whichcorrespond to odd numbers, are outputed by the interrupt handling 3, dueto the addition of FIG. 22(G'), so that driving of a brushless D.C.motor under a condition that the conducting term is determined to be150° by electrical angle, is performed.

FIG. 20 is a flowchart which explains contents of processing of theinterrupt handling 2' in detail. The interrupt handling 2' is acceptedwhen the phase correction timer 18a', started in the interrupt handling1', becomes count-over condition. In step SP1, an inverter mode isadvanced by 1 step, this inverter mode previously determined in thememory 18c'. In step SP2, a voltage pattern corresponding to theadvanced inverter mode is outputed. In step SP3, a timer value (a valuecorresponding to 30°) for the second phase correction timer 18e iscalculated based upon the phase correction value. In step SP4, the timervalue for correction is set to the second phase correction timer 18e. Instep SP5, the second phase correction timer 18e is started. Thereafter,processing is returned to prior processing.

FIG. 21 is a flowchart which explains contents of processing of theinterrupt handling 3 in detail. The interrupt handling 3 is acceptedwhen the second phase correction timer 18e started in the interrupthandling 2', becomes count-over condition. In step SP1, an inverter modeis advanced by 1 step, which inverter mode is previously determined inthe memory 18c'. In step SP2, a voltage pattern corresponding to theadvanced inverter mode is output. Thereafter, processing is returned toprior processing.

The magnetic pole position detection by the amplifier 15, integrator 16and zero-cross comparator 17 which are illustrated in FIG. 14, isdescribed in more detail.

In magnetic pole position detection which is achieved by detecting motorvoltages, a magnetic pole position detection method is employed inelectric equipment such as an air conditioner or the like. This methoduses induced voltages which appear in both upper and lower arms' OFFterm of the conducting interval of 120° by electrical angle. The methodbecomes impossible to detect the induced voltages when high load isemployed and currents are increased so that the magnetic pole positiondetection is impossible to achieve.

When it is assumed that the time period until the current flowing instator windings is cut off, is t, conducting angle of inverters in theterm of 180° by electrical angle is determined to be α (rad), and outputfrequency is f, a condition formula for determining possibility andimpossibility of induced voltage detection, is as follows.

    t<(π-α)/(4πf)

As is apparent from the condition formula, it is understood thatdetection of induced voltage is principally impossible when a conductinginterval of 180° by electrical angle is employed. When a greater torqueis required, an amplitude of a current should be increased. When anamplitude of a current is increased, a residual current due to motorinductance becomes greater. In the worst case, a current flowing in astator winding is not cut off during a 180° term (a term correspondingto 180° by electrical angle). Therefore, an amplitude of a currentshould be limited so that a current flowing in a stator winding issecurely cut off during the 180° term. Consequently, an amplitude of acurrent cannot be increased too much when high speed revolution isperformed and/or when conducting period is lengthened.

When the arrangement illustrated in FIG. 14 is employed, the voltageE_(N-0) at the neutral point 13d of the Y-connected stator windings 13u,13v, 13w becomes the following equation:

    E.sub.N-0 =(1/3){(V.sub.u-0 -E.sub.u-0)+(V.sub.v-0 -E.sub.v-0)+(V.sub.w-0 -E.sub.w-0)}

In other words, the voltage E_(N-0) becomes a sum {refer to FIG. 23(G)}of 3n order higher harmonic components (wherein, n is an integer) whichare included in the inverter output waveforms {refer to FIGS. 23(A),23(B) and 23(C)} and the induced voltage waveforms {refer to FIGS.23(D), 23(E) and 23(F)} of a motor.

Further, the voltage V_(M-0) at the neutral point 14d of the Y-connectedresistors 14u, 14v, 14w becomes the following equation (refer to FIG.23(H)}:

    V.sub.M-0 =(1/3)(V.sub.u-0 +V.sub.v-0 +V.sub.w-0)

Therefore, the 3n order higher harmonic component is taken out byobtaining a difference E_(N-0) -V_(M-0) {refer to FIG. 23(I)} betweenboth voltage s E_(N-0), V_(M-0). The arrangement illustrated in FIG. 14is not limited by the condition formula and is applicable to conductingterm having an arbitrary angle, because both equations are independentof a current. That is, magnetic pole position detection is achievedwithout using a magnetic pole position sensor especially when high speedrevolution is performed and/or when conducting period is lengthened andwhen an amplitude of a current is increased. Also, magnetic poleposition detection is achieved without using a magnetic pole positionsensor especially when a conducting interval of 180° by electrical angleis employed.

In the foregoing, driving and controlling of a brushless D.C. motor isdescribed under only a condition that the brushless D.C. motor is understeady operation. But, the above driving and controlling cannot beachieved when the brushless D.C. motor is stopped, because no inducedvoltages are generated. Therefore, when driving of the brushless D.C.motor is started, three-phase alternating voltage is externally andforcibly supplied to the brushless D.C. motor so that the rotor isrotated by synchronized operation. When the rotor begins its revolution,an induced volatge is generated so that the above driving andcontrolling of the brushless D.C. motor is achieved.

Further, when the conducting interval of 180° by electrical angle isemployed, and when a brushless D.C. motor, in which permanent magnetsare installed interior of a rotor and in which the motor has a specialapplication, is driven under a condition of high revolution and greatload, the motor current and the integration signal of the positiondetector are varied as are illustrated in FIGS. 24(A) and 24(B). It isunderstood that the integration signal is greatly disorder when theconducting interval of 180° by electrical angle is employed, bycomparing the motor current and the integration signal to the motorcurrent and the integration signal {refer to FIGS. 25(A) and 25(B)}which are obtained when the conducting interval of 120° by electricalangle is employed. Of course, a difference signal between voltages isdisorder. Therefore, when a slight varying in load, resonance and thelike in the driving system of the inverters and the brushless D.C. motorare generated, a point appears at which the integration signal is notzero-crossed due to the disorder so that the position signal is notobtained and the brushless D.C. motor may step out. The motor currentillustrated in FIG. 24(A) is different from the current waveformsillustrated in in FIGS. 2(A), 12(B) and 13(B). The difference is causedby difference in motor application. Provided that such disadvantage arerarely generated.

To dissolve such disadvantage which is generated under a specialcondition, so that reliability of the apparatus for driving andcontrolling the brushless D.C. motor is improved, the conductinginterval should be determined to be more than 120° and less than 180° byelectrical angle. FIGS. 26 through 30 illustrate motor currents andintegration signals which correspond to cases that the conductinginterval is determined to be 130°, 140°, 150°, 160°, and 170° byelectrical angle, respectively. As is apparent from those figures,disorder in integration signals are eliminated. Further, operatingranges of a compressor (a compressor which employs a brushless D.C.motor as a driving source), and motor efficiencies of the brushless D.C.motor are illustrated in FIGS. 31 and 32 which correspond to cases thatthe conducting interval is determined to be 130°, 140°, 150°, and 180°by electrical angle, respectively, and that the input currents aredetermined to be the same to one another. As is apparent from FIG. 31,the operating ranges scarcely vary when the conducting interval isdetermined to be 140°-170° by electrical angle. Also, as is apparentfrom FIG. 32, lowering in the motor efficiency is less than 1% when theconducting interval is determined to be 140°-170° by electrical angle.Therefore, it is preferable that the conducting interval is determinedto be 140°-170° by electrical angle. In this case, the abovedisadvantage is securely prevented from occurrence by scarcely reducingthe operating range. The results in only scarcely lowering the motorefficiency, so that the reliability is remarkably improved.

Further, an arrangement may be employed instead of the positiondetection circuitry which includes the amplifier 15, integrator 16 andzero-cross comparator 17. The arrangement is illustrated in FIG. 33(A),and has an amplifier 115 which is supplied the voltage at the neutralpoint 13d (refer to FIG. 14) to a non-reversed input terminal through aresistor 115a, and is supplied the voltage at the neutral point 14d(refer to FIG. 14) to a reversed input terminal. And, a resistor 115band a capacitor 116b are connected in parallel between an outputterminal and the reversed input terminal of the amplifier 115.Furthermore, an arrangement which is illustrated in FIG. 33(B) may beemployed. The arrangement is obtained by adding an amplifier 117 to thearrangement illustrated in FIG. 33(A). The which amplifier 117 has aresistor which is connected between an output terminal and a reversedinput terminal. In this arrangement, an output signal from the amplifier115 is supplied to the reversed input terminal of the amplifier 117through a resistor. Further, an arrangement which is illustrated in FIG.33(C) may be employed. The arrangement is obtained by switching theamplifiers 115 and 117, as they appear in FIG. 33(B), with one another.When the arrangement illustrated in FIG. 33(C) is employed, the voltageat the neutral point 13d may be supplied to the reversed input terminalof the amplifier 117 through a resistor and the voltage at a neutralpoint 14d may directly be supplied to a non-reversed input terminal ofthe amplifier 117. When one of those arrangements is employed, operationwhich is similar to that of a corresponding portion which is illustratedin FIG. 14 is achieved.

Further, reducing in power consumption is required for an electricalequipment such as air conditioner, vacuum cleaner, electrical washer andthe like, and a brushless D.C. motor and an inverter which have drawnattention in recent years, are going to be employed. When the apparatusfor driving and controlling a brushless D.C. motor according to thepresent invention is applied to those electrical equipments, powerconsumption is further reduced in comparison to conventional electricalequipments which employ a brushless D.C. motor and inverters.

Possibility in Industrial Utilization

The present invention performs improvement in efficiency and enlargementin operating range of a brushless D.C. motor which is employed as adriving source in various applications.

What is claimed is:
 1. A brushless D.C. motor driving and controllingmethod for driving a brushless D.C. motor using voltage-fed inverters,said method comprising the steps:setting a conducting interval of saidvoltage-fed inverters to a predetermined interval which is more than120° and equal or less than 180° by electrical angle; and supplyingoutput voltage from said voltage-fed inverters to said motor.
 2. Abrushless D.C. motor driving and controlling method as set forth inclaim 1, wherein said method further comprises the steps of obtainingoutputs of said voltage-fed inverters and modulating said outputs tooutput pulse signals, each pulse signal having constant pulse widthswithin an entire conducting interval.
 3. A brushless D. C. motor drivingand controlling method as set forth in claim 1 wherein said methodfurther comprises the steps of providing a rotor which includespermanent magnets in the interior thereof as a rotor of said brushlessD.C. motor.
 4. A brushless D.C. motor driving and controlling method asset forth in claim 3, wherein said method further comprises the steps ofcontrolling said voltage-fed inverters so that a controlled outputvoltage therefrom has a phase that is advanced from the phase of theinverter output voltage with respect to induced voltage of saidbrushless D.C. motor, said phase with respect to induced voltage causingthe motor current and the induced voltage of said brushless D.C. motorto have the same phase.
 5. A brushless D.C. motor driving andcontrolling method as set forth in claim 1, wherein said conductinginterval of said voltage-fed inverters is determined to be 180° byelectrical angle.
 6. A brushless D.C. motor driving a controlling methodas set forth in claim 1, wherein said method further comprises the stepsof:obtaining a first voltage at a neutral point by connecting one end ofeach of plural resistors together and connecting the other end of eachof said resistors to each output terminal of said voltage-fed inverters,obtaining a second voltage at a neutral point by connecting one end ofeach stator winding of said brushless D.C. motor together, and detectinga magnetic pole position of said rotor of said brushless D.C. motorbased upon a difference between said first voltage and said secondvoltage.
 7. A brushless D.C. motor driving and controlling method as setforth in claim 6, wherein said conducting interval of said voltage-fedinverters is more than 120° and less than 180° by electrical angle.
 8. Abrushless D.C. motor driving and controlling method as set forth inclaim 6, wherein said conducting interval of said voltage-fed invertersto be a predetermined interval which is equal or more than 140° andequal or less than 170° by electrical angle.
 9. A brushless D.C. motordriving and controlling apparatus for driving a brushless D.C. motor,said apparatus comprising:a plurality of voltage-fed invertersconnectable to a brushless D.C. motor; and a conducting intervaldetermining means for determining a conducting interval of saidvoltage-fed inverters to be a predetermined interval which is more than120° and equal or less than 180° by electrical angle.
 10. A brushlessD.C. motor driving and controlling apparatus as set forth in claim 9,including a modulating means for modulating outputs from saidvoltage-fed inverters so as to provide output pulse signals, each pulsesignal having constant pulse widths within an entire conductinginterval.
 11. A brushless D.C. motor driving and controlling apparatusas set forth in claim 9, wherein said apparatus includes a rotor withpermanent magnets in the interior of said rotor as a rotor of abrushless D.C. motor controlled by said apparatus.
 12. A brushless D.C.motor driving and controlling apparatus as set forth in claim 10,further comprising a phase controlling means for controlling saidvoltage-fed inverters so that the phase of controlled inverter outputvoltage is advanced from the phase of the inverter output voltage withrespect to induced voltage of a brushless D.C. motor controlled by saidapparatus, said phase with respect to induced voltage causing the D.C.motor current and the induced voltage of a brushless D.C. motorcontrolled by said apparatus to be the same.
 13. A brushless D.C. motordriving and controlling apparatus as set forth in claim 9, wherein saidconducting interval determining means determines a conducting intervalof said voltage-fed inverters to be 180° by electrical angle.
 14. Abrushless D.C. motor driving and controlling apparatus as set forth inclaim 9, wherein said apparatus further comprisesresistors which eachhave one end connected to each output terminal of each of saidvoltage-fed inverters and which each are connected to one another attheir other end, a difference voltage outputting means for receiving afirst voltage at a neutral point which voltage is obtained by connectingsaid other ends of each of said resistors, and for receiving a secondvoltage at a neutral point which voltage is obtained at the neutralpoint at which stator windings of said brushless D.C. motor areconnected to one another, said difference voltage outputting meansoutputting a difference voltage between said first voltage and saidsecond voltage, and a rotor position detecting means for detecting amagnetic pole position of said rotor of a brushless D.C. motorcontrolled by said apparatus based upon a difference voltage.
 15. Abrushless D.C. motor driving and controlling apparatus as set forth inclaim 14, wherein said conducting interval determining means determinesa conducting interval of said voltage-fed inverters to be apredetermined interval which is more than 120° and less than 180° byelectrical angle.
 16. A brushless D.C. motor driving and controllingapparatus as set forth in claim 14, wherein said conducting intervaldetermining means determines a conducting interval of said voltage-fedinverters to be a predetermined interval which is equal or more than140° and equal or less than 170° by electrical angle.
 17. Electricalequipment comprising:a brushless D.C. motor; and D.C. motor driving andcontrolling apparatus according to claim 9 for driving said brushlessD.C. motor.